In conventional photography, the camera must typically be focused at the time the photograph is taken. The resulting image may have only color data for each pixel; accordingly, any object that was not in focus when the photograph was taken cannot be brought into sharper focus because the necessary data does not reside in the image.
By contrast, light-field images typically encode additional data for each pixel related to the trajectory of light rays incident to that pixel when the light-field image was taken. This data can be used to manipulate the light-field image through the use of a wide variety of rendering techniques that are not possible to perform with a conventional photograph. In some implementations, a light-field image may be refocused and/or altered to simulate a change in the center of perspective (CoP) of the camera that received the image. Further, a light-field image may be used to generate an enhanced depth-of-field (EDOF) image in which all parts of the image are in focus. In some light-field cameras, light-field data are captured through the use of a microlens array adjacent to the image sensor. Each ray of light passes through the microlens array, and is redirected by one of the microlenses to a location on the image sensor that indicates the origin of the ray.
Unfortunately, due to the limitations of manufacturing processes, the exact position and orientation of the microlens array, relative to the image sensor, may vary from one camera to the next. Thus, in order to obtain accurate information from the light-field data regarding the origin of light received by the image sensor, the camera must be properly calibrated based on the actual position and orientation of the microlens array relative to the image sensor.
Certain effects can pose unique challenges for such calibration. For example, if the lens of the light-field image capture device has a strong shading and/or vignetting effect, the calibration image may have significant intensity gradients that make it difficult to properly locate the center of the microlens array. Further, if the aperture of the light-field image capture device causes significant eclipse effects to occur, the center of any given microlens may be difficult to properly locate, due to fact that such eclipse effects may cause microlens portions of a light-field image to have a non-circular shape. Existing calibration techniques do not provide satisfactory solutions to these challenges.